This study is designed to provide knowledge of how polymorphic allelic variation in Drosophila populations is translated through a critical subsystem of the organism (glycolysis) to differences among individuals in fitness traits. The correlation between mutational varation in enzymes involved in glycolysis and variation in the levels of glycolytic intermediate pools and between this pool variation and variation among individuals in fitness traits will be estimated. This research takes advantage of recently developed techniques to measure glycolytic intermediate pools in adult Drosophila. The utilization of measurements of the substrates and products on which enzymes operate will give us a more realistic and statistically more powerful approach (than is possible with allele frequency data collected across populations of a species) in determining the role that inherited enzyme variation plays in determining variation in health and fitness among individuals within a population.